With rapid increase in electronic information dealt with in organizations, such as corporations, many storage systems have been introduced in each of information systems in the organizations and have been in operation. Techniques for enhancing the scalability of a storage system and for facilitating management include a virtualization technique.
For example, Patent Literature 1 discloses a technique called “virtual storage”. The virtual storage is made up of multiple real storages. Each real storage has a virtual storage identifier and a real storage identifier. The virtual storage identifier is an identifier that the real storages constituting the virtual storage commonly have. The real storage identifiers are identifiers unique to the respective real storages that constitute the virtual storage. As to an LU (Logical Unit) that is a logical volume designated by a server in cases of reading and writing, the virtual storage has virtual LUNs (Logical Unit Numbers) and real LUNs. The virtual LUN is an identifier unique in the virtual storage. The real LUN is an identifier unique in the real storage. The characteristics of the virtual storage, for example, allow the multiple real storages to be dealt with apparently as a huge single virtual system. Further, when an old storage is replaced with a new storage, the real storage identifier is changed. In a case where the old storage and the new storage are configured to have the same virtual storage identifier, the server does not recognize the replacement of the storage. Consequently, the storage can be replaced without interruption of operation.
Patent Literature 1 further discloses a technique called ‘capacity virtualization’. The capacity virtualization is also called thin provisioning. According to a capacity virtualization function, a storage system defines a storage area that is called a pool and has a relatively large capacity, and splits the storage area into sections that are called pages. The storage system secures no storage area when defining a logical volume, but allocates a page to a corresponding area when writing to the logical volume actually occurs. At an initial state, the amount of data to be written into the logical volumes is not large in many cases. Consequently, use of the capacity virtualization function can reduce the storage area to be prepared. The timing at which the storage area is allocated is a timing at which writing occurs. Accordingly, a user (administrator) of the storage system is not required to calculate the capacity of the logical volume rigorously, and the user is allowed to define a relatively large capacity instead. Consequently, the management cost can be also reduced.